(a) Field of the Invention
The present invention relates to liquid-crystalline polymers and to liquid-crystalline compounds to be used for preparation of the liquid-crystalline polymers.
More particularly, the present invention relates to liquid-crystalline polymers and liquid-crystalline compounds to be used for preparation of the liquid-crystalline polymers, which liquid-crystalline polymers exhibit ferroelectricity even at temperatures around room temperature, have such high speeds of response to external factors as to enable display of motion pictures. Such liquid-crystalline polymers are useful in optoelectronics fields as various kinds of optical elements, particularly, as those for display devices for desk calculators, clocks and watches, etc., and as those for various electronic optical devices for electronic optical shutters, electronic optical diaphragms, optical modulators, optical-path transfer switches in optical communication systems, memories, liquid crystal printer heads, varifocal lenses, etc. In addition to the above-described advantages, the liquid-crystalline polymers of the present invention have also high practicality in their use as the display elements for large display screens or curved display screens.
(b) Description of the Related Art
Display devices in which low molecular weight liquid crystals are used as their display elements have been widely used for digital display of desk calculators, clocks and watches, etc. In these fields of utilization, the conventional low molecular weight liquid crystals are generally supported between a couple of glass substrates spaced from each other in microns. However, such an adjustment of the space has been practically impossible in production of large display screens or curved display screens. In order to solve the problem, some attempts have been made to develop polymeric liquid crystals so as to render moldability to the liquid crystals themselves. For example, in Japanese Patent Application Kokai Koho (Laid-open) No. 55-21479, Japanese Patent Application Kokai Koho (Laid-open) No. 63-99204, and EP-0184482 disclosed are various kinds of polyacrylate-type ferroelectric, polymeric liquid crystals. Nevertheless, these conventional polymeric liquid crystals have hardly been satisfactory for practical use because of their high temperature ranges where ferroelectricity is exhibited. Further, these polymeric liquid crystals have deficiencies in that their speeds of response in the changes of their transmission intensity to the changes of external factors such as electric field are generally slow.
In Japanese Patent Application Kokai Koho (Laid-open) No. 1-131234 disclosed are polyether-type ferroelectric, polymeric liquid crystals having particular chemical structures which are colorless, exhibit ferroelectricity even at temperatures around room temperature, and have high speed of response to electric field. In spite of their high speed of response to electric field, they still have a problem in that they hardly take bistable state because of their short helical pitches. Further, polymers having two-cyclic skeleton in their mesogenic groups generally have low temperature ranges of SmC* phase (ferroelectric, chiral smectic C phase), and those of polymers having three-cyclic skeleton in their mesogenic radicals are generally high, and therefore, there is a difficulty in their use at temperatures around room temperature.